How can I do this

puzzled.rb

# underpants
data = [
  {a: 1, b: 1, c: 'a'},
  {a: 1, b: 2, c: 'b'},
  {a: 2, b: 2, c: 'c'}
]

# ?
new_data = transform_data(data)

# profit!
new_data[1][1]
# => 'a'
new_data[1][2]
# => 'b'

def transform_data data
  data.each_with_object({}) do |row, hash|
    hash[row[:a]] ||= {}
    hash[row[:a]][row[:b]] = row[:c]
  end
end

@jgaskins

I wrote almost exactly the same code using inject instead of each_with_object...

def transform_data(data)
  data.inject({}) do |hash, row| 
    hash[row[:a]] ||= {} 
    hash[row[:a]][row[:b]] = row[:c] 
    hash
  end
end

I think yours is a little tidier, tho, without having to return hash from each block.

Thanks! :)

I only use inject if I'm not modifying anything. If I'm doing any sort of mutation, I use each_with_object. When building state from scratch, mutation is just faster, so I use each_with_object waaaaay more than inject.